1. Field of the Invention
The present invention relates generally to coiled tubing operations. In another aspect, the present invention concerns a system for simultaneously translating and rotating coiled tubing in a bore. In a further aspect, the present invention concerns a system which employs simultaneously translating and rotating coiled tubing to drill a borehole in a subterranean formation.
2. Description of the Prior Art
Oil and gas wells have traditionally been drilled using a string of substantially ridged, rotatable steel pipe sections having a drill bit attached to the end of the string. A significant disadvantage of this type of rotary drilling system is the amount of time consumed when it is necessary to remove the drill string from the borehole in order to perform operations such as replacing the drill bit or setting casing. Because individual sections of pipe must be unscrewed when removing the drill string from the borehole, it can take hours, or even days, to remove the drill string from the borehole. Further, because individual sections of pipe must be screwed together when reinserting the drill string into the borehole, it can consume additional hours, or even days, to reinsert the drill string into the borehole.
In recent years, drillers have discovered an alternative to traditional rotary drilling. This alternative employs coiled tubing rather than rigid sections of steel pipe. Coiled tubing is a continuous length of flexible tubing which can be stored on a reel. Each reel may contain 10,000 feet or more of continuous coiled tubing. Coiled tubing can be used to drill a borehole by attaching a hydraulic motor and drill bit to its downhole end and then charging pressurized drilling fluid to the tubing. The pressurized drilling fluid drives the hydraulic motor which, in turn, rotates the drill bit. The drill bit and hydraulic motor are lowered into the borehole as the coiled tubing is spooled off the reel to thereby drill the borehole.
A significant advantage of coiled tubing drilling is that the coiled tubing can be raised and lowered in the borehole at rates up to ten times faster than those possible with conventional rotary drilling techniques. This increased xe2x80x9ctrippingxe2x80x9d speed is primarily attributable to the fact that coiled tubing can be tripped without screwing or unscrewing individual sections. A further advantage of coiled tubing drilling is the enhanced ability to control downhole pressure. This ability to control downhole pressure provides for numerous advantages associated with underbalanced drilling.
However, one significant disadvantage of conventional coiled tubing drilling is the inability to rotate the tubing in the borehole. The fact that the coiled tubing does not rotate relative to the borehole means that all of the energy for rotating the drill bit must be supplied by the pressurized drilling mud which drives the hydraulic motor. Further, lack of rotation of the coiled tubing in the borehole causes increased friction between the walls of the borehole and the coiled tubing. This increased friction can make it difficult to translate the tubing in the borehole. Further, the increased friction between the coiled tubing and the borehole may require more frequent tripping of the tubing.
In accordance with an embodiment of the present invention, an apparatus for shifting an elongated flexible working member between a wound position on a reel and an extended position in a receiving opening is provided. The apparatus comprises a guide member, a first powering device, and a second powering device. The guide member is adapted to direct the working member between the wound position and the extended position. The first powering device is adapted to selectively rotate the reel on a reel axis. The second powering device is adapted to selectively move the guide member relative to the reel around the reel axis.
In accordance with another embodiment of the present invention, an apparatus for selectively shifting coiled tubing into and out of a borehole extending into a subterranean formation is provided. The apparatus comprises a reel and a guide member. The reel is adapted to store the coiled tubing in a wound position thereon. The reel includes a reel opening extending therethrough. The guide member is adapted to direct the coiled tubing from the wound position to a position in which the coiled tubing is aligned for extension through the reel opening.
In accordance with a further embodiment of the present invention, a drilling rig for drilling a borehole in a subterranean formation using coiled tubing is provided. The coiled tubing is at least partially disposed in a wound position on a reel. The reel defines a reel axis and a reel opening extending through the reel along the reel axis. The drilling rig comprises a reel support, a guide member, and a power injector. The reel support is adapted to support the reel in a position wherein the reel axis is at least substantially upright. The guide member is adapted to direct the coiled tubing between the wound position and a position in which the coiled tubing is aligned for extension through the reel opening. The power injector is operable to translate the tubing relative to the guide member.
In accordance with a still further embodiment of the present invention, a method of shifting an elongated flexible tubing in and out of a bore is provided. The method comprises the steps of: (a) unwinding a length of the tubing off of a reel around which the tubing is wound; and (b) directing the unwound portion of the tubing through an opening in the reel and into the bore.
In accordance with an even further embodiment of the present invention, a method of drilling a borehole and subterranean formation is provided. The method comprises the steps of: (a) positioning a rotatable reel so that an axis of rotation of the reel is at least substantially upright, said reel having a reel opening which extends through the reel at least substantially along the reel axis of rotation; (b) unwinding a portion of a coiled tubing off of the reel; (c) positioning at least a portion of the unwound coiled tubing in a guide member which directs the unwound coiled tubing generally downward through the reel opening and into an extended position; (d) rotating the guide member relative to the subterranean formation to thereby cause rotation of the coiled tubing the extended position relative to the subterranean formation; and (e) simultaneously with step (d), actuating a power injector to thereby cause translation of the coiled tubing in the extended position relative to the subterranean formation.